Basics about Efficiency Calibration of Gamma Detectors
In this exercise you are to do an efficiency calibration of a Ge-detector. The efficiency to any
detector is dependent on quantities such as the
To calibrate a detector we must also take into consideration that a ray will not necessarily be
emitted every time the source disintegrate. The frequency rays are emitted can be found in tables
and is given as the intensity, usually symbolised with I . The formula we use to calculate the
efficiency then looks like this:
Notice that we have indexed the and R with an E to indicate that these are energy dependant. Since
all the absorbation processes for radiation is strongly dependent on the -ray energy, the detector
efficiency will also be dependent on energy. Thus, to calibrate a detector we must use a range of
sources with energies that cover the range of energy we are planing to measure in. The efficiency
calibration will then look like something in Figure 1. The most common range to measure radiation
in is from about 50 keV and up to about 1-2 MeV. From Figure 1 we can se that the range between
about 200 keV and up to 2 MeV is nearly linear in double-logarithmic scale. Below 200-250 keV
this is not true.